An invasion of a species is defined as the introduction, establishment, and subsequent spread of that species in a geographic area different from its original or native geographical range. Once a species has been introduced into a new habitat, it can be naturalized; that is, it can adapt to the new environment and expand its population, usually producing negative effects on native species and on the whole ecosystem structure. Not all human-induced introductions of species are successful, and invasive populations can become extinct shortly or even after a long time. There are two aspects to consider in the ecological study of invasions: (1) the susceptibility of a territory to an alien invasion (i.e., the suitability of a territory to the ecological requirements of an invasive ...